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In a lot of photos I've seen here and elsewhere of hot water home heating systems with multiple zones, each zone has its own circulator.

In my two-zone system there is one circulator, with a zone valve on the feed to each zone and a common return pipe. It seems to work well. There is very little bleed between zones, and when both zones call for heat the radiators all get hot.

Is there a benefit to multiple circulators?

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Systems engineering tradeoffs.

In general, one pump per zone will cost more, but can (in theory) be matched more perfectly to the zone (but there are only a few typical sizes of pump, so that may not be all that perfect, after all.)

One pump to feed them all will be the right sized pump as some set of zones, and more or less than ideal with other sets open or closed - however, there's a functional range, and if properly designed either method can be operated in safe ranges.

In general, most heating system designers are not too concerned with how much power the pumps use, (they don't pay for it, and it's not generally obvious to the end-user) which can be another downside (for the end-user) of a particularly inappropriate choice of pump(s) for the job. Designers are concerned with not running the pumps into cavitation which can destroy them, and the fluid velocity in the pipes. In some cases more pumps may mean less wasted power, but without working that out the greater initial expense of more pumps tends to be what's controlling.

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On the systems I have worked on the systems with multiple floors each floor had independent zones. These were separately controlled and pumped I have seen a very similar one with a single pump (I was wiring the controls and the valves) I asked the owner and he said it could be done with one but air bubbles were harder to purge and that was the reason. Both zones were on the same water heater /boiler.

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